Rolling body screw device

ABSTRACT

A return pipe is constituted by combining a pair of return pipe halves split along a non-load passage. A pipe hold down member is fixed to a nut member so as to be astride the return pipe, fixing the return pipe to the nut member. A flange portion is formed on each of the return pipe halves, while a pair of fixing leg portions covering the flange portion of each return pipe half is formed on the pipe hold down member. Fastening members pass through the fixing leg portions of the pipe hold down member and the flange portion of the return pipe halves and are fastened to the nut member. When the fixing leg portions of the pipe hold down member are fixed to the nut member by the fastening members, an engagement portion of the pipe hold down member is configured to tighten the pair of the return pipe halves in the direction where split faces of the return pipe halves abut against each other.

TECHNICAL FIELD

The present invention relates to a rolling body screw device in which anut member is threadedly engaged with a screw shaft through theintermediation of rolling bodies such as balls or rollers, and whichconverts a rotary movement of a motor to a linear movement in, forexample, a worktable of a machine tool, and more specifically, to arolling body screw device in which a substantially U-shaped return pipeis attached to a nut member to form an endless circulation path for therolling bodies.

BACKGROUND ART

There are known various types of rolling body screw device in which anendless circulation path for rolling bodies is formed by using aso-called return pipe. Such a rolling body screw device is equipped witha screw shaft having a helical rolling groove, a nut member having ahelical load rolling groove opposed to the above-mentioned rollinggroove and adapted to be threadedly engaged with the screw shaft throughthe intermediation of rolling bodies, and a return pipe attached to thisnut member to form an endless circulation path for the rolling bodies.

The return pipe is equipped with a pair of leg portions to be insertedinto the nut member and a communication path portion connecting the legportions and is formed in a substantially U-shaped sectionalconfiguration, wherein there is formed, from one leg portion to theother leg portion, a non-load passage in which rolling bodies can roll.On the other hand, the nut member has a pair of rolling body passingholes for the insertion of the leg portions of the return pipe that areformed with the central axis of the nut member therebetween, with therolling body passing holes being open tangentially with respect to theinner peripheral surface of the nut member. Further, these rolling bodypassing holes are formed so as to be spaced apart from each other by adistance corresponding to several turns of the load rolling groove. Whenthe leg portions of the return pipe are inserted into the rolling bodypassing holes, each leg portion protrudes slightly from the innerperipheral surface of the nut member, scooping up the rolling bodiesfrom the rolling groove of the screw shaft into the return pipe. Thus,the rolling bodies that have been rolling under load between the rollinggroove of the screw shaft and the load rolling groove of the nut memberare relieved of the load and are detached from the rolling groove of thescrew shaft when they reach the position where the leg portions of thereturn pipe protrude, and roll inside the return pipe under a non-loadstate to be returned to the rolling groove through a distancecorresponding to several turns. That is, by attaching the return pipe tothe nut member, there is formed an endless circulation path for therolling bodies.

As an example of the return pipe, there is known one obtained by bendingan iron tube into a substantially U-shape. This, however, involves highproduction cost, and is subject to variation in dimension whenperforming the bending.

Another known example of the return pipe is formed by splitting a returnpipe into two along a plane including the non-load passage for therolling bodies to obtain a pair of return pipe halves. Formed in eachreturn pipe half is a non-load passage of a substantially semicircularsectional configuration; by causing these return pipe halves to abuteach other, a non-load passage for the rolling bodies is completed.

As shown in FIG. 7, these return pipes are fixed to a nut member 101 byusing a pipe hold down member 100 formed of a metal plate. The pipe holddown member 100 is fixed to the nut member 101 by screws so as to beastride the return pipe 102, whereby the return pipe 102 is fixed to thenut member 101, with a pair of leg portions 103, 103 inserted intorolling body passing holes 104, 104.

However, the inner diameter dimension of the non-load passage providedin the return pipe is set somewhat larger than the outer diameterdimension of the rolling bodies, so that when the rolling bodiesactually circulate through the endless circulation path provided in thenut member, the rolling bodies repeatedly collide with the innerperipheral wall of the return pipe when rolling in the non-load passage.In the case in which the return pipe is formed through abutment of apair of return pipe halves, the impact force when the rolling bodiescollide with the inner peripheral wall of the return pipe acts as aforce to push open the abutment surfaces of the return pipe halves, and,during the circulation of the rolling bodies, this force is continuouslyacting on the return pipe. Thus, as the operation time of the rollingbody screw device is accumulated, a gap is generated between theabutment surfaces of the return pipe halves, so that there is a fear ofcausing a trouble of the rolling bodies to be rolled out through thisgap.

In particular, in the case of a rolling body screw device for higherload and larger thrust, the rolling bodies collide with the innerperipheral wall of the return pipe so much the more vigorously, so thatthe gap is likely to be generated at an early stage, which makes itnecessary to reliably effect the abutment of the pair of return pipehalves against the impact force due to this collision.

DISCLOSURE OF THE INVENTION

The present invention has been made in view of the above problem. It isan object of the present invention to provide a rolling body screwdevice, in which, in forming a return pipe through abutment of a pair ofreturn pipe halves obtained through splitting along a non-load passagefor the rolling bodies, the abutment of these return pipe halves iseffected reliably, whereby generation of a gap between the abutmentsurfaces of the return pipe halves during circulation of the rollingbodies is prevented, making it possible to withstand a long-term useeven under a condition of high load and large thrust.

To achieve the above object, in the rolling body screw device of thepresent invention, a return pipe is formed through combination of a pairof return pipe halves obtained by splitting along a non-load passage,and a pipe hold down member is fixed to a nut member so as to be astridethe return pipe to thereby fix the return pipe to the nut member.Further, formed on each return pipe half is a flange portion protrudingin a direction crossing the non-load passage, and formed on the pipehold down member are an engagement portion equipped with a recess to befit-engaged with the return pipe and a pair of fixing leg portionscovering the flange portions of each of the return pipe halves, withfastening members being fastened to the nut member through the fixingleg portions of the pipe hold down member and the flange portions of thereturn pipe halves. When the fixing leg portions of the pipe hold downmember are fixed to the nut member by the fastening members, theengagement portion of the pipe hold down member exerts a tighteningeffect such that the split faces of the pair of return pipe halves arebiased to abut each other.

According to the present invention, constructed as described above, whenthe rolling bodies circulate in the non-load passage path providedinside the return pipe, even if a force attributable to the collision ofthe rolling bodies with the inner peripheral wall of the return pipe isexerted on the abutment surfaces of the pair of return pipe halves so asto push them open, it is possible to firmly maintain the abutment stateof the return pipe halves by utilizing the tightening force of the pipehold down member. As a result, it is possible to prevent generation of agap between the pair of return pipe halves, making it possible toachieve an increase in the service life of the return pipe even whenused under a condition of high load and large thrust.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a linear actuator including a rollingbody screw device to which the present invention is applied.

FIG. 2A is a perspective view of a return pipe of a rolling body screwdevice to which the present invention is applied.

FIG. 2B is a plan view of the return pipe of the rolling body screwdevice to which the present invention is applied.

FIG. 2C is a front view of the return pipe of the rolling body screwdevice to which the present invention is applied.

FIG. 3 is a longitudinal sectional view of the linear actuator shown inFIG. 1.

FIG. 4A is a perspective view showing a relationship between the returnpipe shown in FIG. 2 and a pipe hold down member.

FIG. 4B is a plan view showing the relationship between the return pipeshown in FIG. 2 and the pipe hold down member.

FIG. 5 is a front view of the pipe hold down member of the presentinvention.

FIG. 6 is a plan view showing the direction in which the tighteningforce of the pipe hold down member is exerted.

FIG. 7 is a perspective view of the mounting structure of a conventionalreturn pipe.

DESCRIPTION OF SYMBOLS

10 . . . outer rail, 20 . . . screw shaft, 21 . . . plurality of balls,30 . . . inner block, 40 . . . return pipe, 50 . . . return pipe halves,51 . . . abutment surface, 52 . . . flange portions, 60 . . . pipe holddown member, 62 . . . engagement portion, 63 . . . fixing leg portions

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, the rolling body screw device of the present inventionwill be described in detail with reference to the accompanying drawings.

FIG. 1 shows a linear actuator 1 including a rolling body screw deviceto which the present invention is applied. The linear actuator 1 iscomposed of an outer rail 10 formed as a channel with a recessed groove11, a screw shaft 20 rotatably provided in the recessed groove 11 of theouter rail 10, and an inner block 30 having a through-hole through whichthe screw shaft 20 is passed and arranged inside the recessed groove 11of the outer rail 10.

The inner block 30 is mounted to the outer rail 10 through theintermediation of a plurality of balls 31, and the inner block 30 isequipped with an endless circulation path through which the balls 31circulate. As a result, the inner block 30 can freely reciprocate insidethe recessed groove 11 of the outer rail 10.

Further, inner block 30 is threadedly engaged with the screw shaft 20through the intermediation of a plurality of balls 21, thus forming aball screw device. The screw shaft 20 is rotatably supported by supportbrackets (not shown) provided at the both longitudinal ends of the outerrail 10, and is rotated by a motor (not shown). As a result, the innerblock 30 advances and retracts within the recessed groove 11 of theouter rail 10 by an amount corresponding to the rotating amount of thescrew shaft 20, making it possible to place a movable body such as atable mounted on the inner block 30 at a predetermined position.

Formed in the outer peripheral surface of the screw shaft 20 is ahelical ball rolling groove 22, and formed in the inner peripheralsurface of the through-hole of the inner block 30 is a load rollinggroove 32 opposed to the ball rolling groove 22. The ball rolling groove22 and the load rolling groove 32 are opposed to each other to form aload rolling path of the balls 21; when the screw shaft 20 rotates, theballs 21 roll within the load rolling path while giving load thereto.The section of the ball rolling groove 22 formed in the screw shaft 20has a Gothic-arch-like configuration constructing of a combination oftwo arcs with a radius of curvature somewhat larger than the radius ofthe balls 21, and the load rolling groove 32 on the side of the innerblock 30 is also formed in a Gothic-arch-like configuration, and theballs 21 roll within the load rolling passage while in four-pointcontact with the ball rolling groove 22 and the load rolling groove 32.A pre-load is imparted to the balls 21 rolling inside the load rollingpassage, so that, when the inner block 30 is moved through rotation ofthe screw shaft 20, it is possible to prevent generation of backlashbetween the screw shaft 20 and the inner block 30 and to enhance thepositioning accuracy in the repeated reciprocating movement of the innerblock 30. As the method of imparting a pre-load, there is adopted, forexample, a method in which balls (over-size balls) with a diameterslightly larger than the gap between the screw shaft 20 and the innerblock 30 are selected, filling the load rolling passage.

Further, mounted to the inner block 30 is a return pipe 40 establishingcommunication/connection between the ends of the load rolling passage.The return pipe 40 has a pair of leg portions 41, 41 and is formed in asubstantially U-shaped configuration, having therein a non-load passagewith an inner diameter slightly larger than the diameter of the balls21. As shown in FIG. 3, the return pipe 40 is attached to the lowersurface side of the inner block 30, that is, to the surface thereofopposed to the base portion lOa of the outer rail 10. Formed in thelower surface of the inner block 30 are a pair of ball passing holes tobe fit-engaged with the leg portions 41 of the return pipe 40, and thedistal end portions of the leg portions 41 of the return pipe 40 extendthrough the ball passing holes to slightly protrude into thethrough-hole of the inner block 30, the balls 21 that come rollingthrough the ball rolling groove 22 of the screw shaft 20 beingaccommodated in the non-load passage of the return pipe 40. The pair ofball passing holes into which the leg portions 41 of the return pipe 40are inserted is formed so as to be spaced apart from each other by adistance corresponding to several turns of the helical load rollingpath.

Thus, when the return pipe 40 is attached to the inner block 30,communication/connection is established between the both ends of theload rolling path through the non-load passage of the return pipe 40,thus completing an endless circulation path for the balls 21. Then, whenthe screw shaft 20 rotates relative to the inner block 30, the pluralityof balls 21 arranged in the endless circulation path circulate throughthe endless circulation path.

Further, the return pipe 40 is fixed to the inner block 30 by a pipehold down member described below. The pipe hold down member will bedescribed in detail below.

FIGS. 2A, 2B, and 2C show the return pipe 40 in detail. The return pipe40 constructed of a pair of return pipe halves 50, 50 having the sameshape and dimension formed by injection molding of synthetic resin andabutting and opposed to each other, with the abutment surfaces 51 beingbonded together by welding or the like. The return pipe 40 has a pair ofleg portions 41 to be inserted into the ball passing holes of the innerblock 30, and a communication passage portion 42 connecting the legportions 41, and is formed in a substantially U-shaped configuration;the configuration of the section of the communicating passage portion42, protruding to the lower surface of the inner block 30, taken in adirection perpendicular to the passing direction of the balls 21 issubstantially rectangular, whereas the pair of leg portions 41, 41 areformed in a substantially cylindrical configuration. Further, at thedistal ends of the pair of leg portions 41, 41, there are formedscoop-up portions 43 for the balls 21, and by protruding the scoop-upportions 43 from the inner peripheral surface of the through-hole of theinner block 30, it is possible to accommodate the balls 21 rolling inthe ball rolling groove 22 of the screw shaft 20 in the non-load passageof the return pipe 40.

Abutment surfaces 51 of a pair of return pipe halves 50, 50, that is,the split faces of the return pipe 40 are formed along the longitudinaldirection of the communication passage portion 42; strictly speaking,however, they are slightly inclined with respect to the longitudinaldirection of the communication passage portion 42. Formed integrallywith each return pipe half 50 is a flange portion 52 for fixing thereturn pipe 40 to the inner block 30. The flange portions 52 protrudesidewise from the communication passage portion 42, that is, in adirection crossing the non-load passage; as shown in FIG. 2B, in thestate in which the pair of return pipe halves 50, 50 abut each other,the pair of flange portions 52, 52 are situated at different positionswith respect to the longitudinal direction of the communication passageportion 42. Further, each flange portion 52 has a cutout portion 54 intowhich a fixing bolt 53 as a fastening member is to be inserted.

FIGS. 4A and 4B show a state in which a pipe hold down member 60 isattached to the return pipe 40. The pipe hold down member 60 is formedby bending a metal plate, and, by fastening the fixing bolts 53 to theinner block 30, it is fixed to the inner block 30 so as to be astridethe return pipe 40, fixing the return pipe 40 onto the inner block 30.The pipe hold down member 60 is provided with an engagement portion 62equipped with a recess 61 to be engaged with the return pipe 40, and, apair of fixing leg portions 63, 63 are formed at the both ends of theengagement portion 62 so as to be continuous thereto, with each fixingleg portion 63 being formed so as to overlap the flange portion 52 ofthe return pipe half 50 to cover the same.

Each fixing leg portion 63 has a through-hole 64 through which thefixing bolt 53 is to be passed, and the through-holes 64 overlap thecutout portions 54 formed in the flange portions 52 of the return pipehalves 50. Thus, as shown in FIGS. 4A and 4B, when the fixing bolts 53are fastened to the inner block 30 from above the fixing leg portions63, it is possible to fix the pipe hold down member 60 and the returnpipe 40 together to the inner block 30. In particular, the return pipehalves 50 are formed of synthetic resin, so that, when the fasteningbolts 53 are directly fastened from above the flange portions 52, thehead portions of the fixing bolts 53 will cut into the flange portions52, which means there is a fear of the return pipe 40 not being fixedwith sufficient firmness. However, by covering the flange portions 52 ofthe return pipe halves 50 with the fixing leg portions 63 of the metalpipe hold down member 60, and fastening the fixing bolts 53 from abovethe same, it is possible to exert the fastening force of the fixingbolts 53 sufficiently on the flange portions 52 of the return pipehalves 50, making it possible to firmly secure the return pipe 40 inposition.

FIG. 5 is a diagram showing the specific configuration of the pipe holddown member 60. The pair of fixing leg portions 63, 63, with which thepipe hold down member 60 is equipped, are formed so as to be inclinedsuch that each of their distal end portions extends away from the flangeportions 52 of the return pipe halves 50. That is, after the engagementportion 62 of the pipe hold down member 60 has been fit-engaged with thereturn pipe 40, in the state in which the fixing bolts 53 have not beenfastened yet, there are formed, as shown in FIG. 5,wedge-like gaps 65between the distal end portions of the fixing leg portions 63 and theflange portions 52. In this embodiment, the pipe hold down member 60 isformed such that the engagement portion 62 and the fixing leg portions63 are at an acute angle α with respect to each other.

By thus forming the wedge-like gaps 65 between the fixing leg portions63 of the pipe hold down member 60 and the flange portions 52 of thereturn pipe halves 50, when the fixing bolts 53 are fastened from abovethe fixing leg portions 63 to forcibly bring the fixing leg portions 63and the flange portions 52 into close contact with each other, theengagement portion 62 of the pipe hold down member 60 undergoes elasticdeformation so as to tighten the return pipe 40. As a result, the pairof return pipe halves 50, 50 opposed to each other are tightened fromoutside through the deformation of the pipe hold down member 60, and thetwo are caused to firmly abut each other at the split faces 51 thereof.

Thus, solely by fastening the fixing bolts 53 to fix the pipe Hold downmember 60, it is possible to cause the return pipe halves 50, 50 tofirmly abut each other; thus, even when the balls 21 roll Vigorouslythrough the non-load passage of the return pipe 40, it is possible theprevent generation of a gap between the abutment surfaces 51 of thereturn pipe halves 50, 50.

Further, the flange portions 52 formed on each of the return pipe halves50, 50 are situated and protruded at positions deviated from each otherwith respect to the longitudinal direction of the non-load passage, andas shown in FIG. 4B, the pipe hold down member 60 is fixed so as to beobliquely astride the return pipe 40. Thus, as shown in FIG. 6, theabove-mentioned fastening force F of the pipe hold down member 60 actsas a couple of forces on the return pipe 40, making it possible to causethe pair of return pipe halves 50, 50 to abut each other more firmly.

Further, by making the width t of the recess 61 of the engagementportion 62 of the pipe hold down member 60 slightly smaller than thewidth of the return pipe 40, and by forming the recess 61 so that therecess slightly expands toward the return pipe 40, as described above,when the fixing bolts 53 are fastened from above the fixing leg portions63 of the pipe hold down member 60, it is possible to cause theengagement portion 62 to tighten the return pipe 40 more strongly, andto cause the return pipe halves 50, 50 to abut each other more firmly.

Thus, in accordance with the present invention, when the pipe hold downmember 60 is fixed to the inner block 30 by using the fixing bolts 53constituting the fastening members, the pipe hold down member 60tightens the return pipe 40, and the return pipe halves 50, 50 opposedto each other are caused to abut each other firmly. As a result, even ifthe balls 21 roll vigorously through the non-load passage in the returnpipe 40, no gap is generated between the abutment surfaces 51 of thereturn pipe halves 50, making it possible to achieve an increase in theservice life of the return pipe 40. Further, even a return pipe formedof synthetic resin, which is subject to deformation, can be used in aball screw device of high load and large thrust.

While in the above embodiment balls are used as the rolling bodies, itis also possible to apply rollers such as cylindrical rollers. Further,while in the above example the nut member is shown as an inner block ofa substantially rectangular sectional configuration, the presentinvention is also applicable to a cylindrical nut member.

1. A rolling body screw device, comprising: a plurality of rollingbodies; a screw shaft having in an outer peripheral surface thereof ahelical rolling groove in which the rolling bodies roll; a nut memberhaving a through-hole through which the screw shaft is passed and havingin an inner peripheral surface of the through-hole a helical loadrolling groove forming a load rolling path for the rolling bodiestogether with the rolling groove; a return pipe having a non-loadpassage for the rolling bodies, the return pipe having a pair of returnpipe halves split in the direction in which the non-load passageextends, with communication being established between both ends of theload rolling path to form in the nut member an endless circulation pathfor the rolling bodies; a pipe hold down member fixing the return pipeto the nut member so as to be astride the return pipe; and fasteningmembers for fixing the pipe hold down member to the nut member, whereineach return pipe half has a flange portion protruding in a directioncrossing the non-load passage, whereas the pipe hold down member has anengagement portion equipped with a recess to be fit-engaged with thereturn pipe and a pair of fixing leg portions covering the flangeportions of the return pipe halves, with the fastening members beingpassed through the fixing leg portions of the pipe hold down member andthe flange portions of the return pipe halves to be threadedly engagedwith the nut member; and wherein, when the fixing leg portions of thepipe hold down member are fixed to the nut member by the fasteningmembers, the engagement portion of the pipe hold down member tightensthe pair of the return pipe halves so as to cause the split faces of thereturn pipe halves to abut each other, and wherein the pair of thefixing leg portions provided on the pipe hold down member are formedsuch that their distal end portions are inclined so as to extend awayfrom the flange portions of the return pipe halves; and that, when thepair of the fixing leg portions are forcibly fixed to the flangeportions of the return pipe halves by the fastening members, theengagement portion of the pipe hold down member undergoes elasticdeformation so as to tighten the return pipe.
 2. A rolling body screwdevice according to claim 1, wherein the pipe hold down member is formedby bending a metal plate.
 3. A rolling body screw device according toclaim 1, wherein the pipe hold down member is arranged so as to beastride the return pipe crossing the split faces of the return pipehalves obliquely; and that the force with which the engagement portionof the pipe hold down member tightens the return pipe halves acts on thepipe hold down member as a couple of forces.